The larva itself is the basis for the pokemon Pineco / Forretress and Burmy / Wormadam - Mothim, so my mind was already on pokermanz - but then you talk about a dragon which starts in a larval form, which puts one in mind of Trapinch / Vibrava / Flygon (or, if one wants to look at it crosswise, Dratini / Dragonair / Dragonite).

Pokemon aside, bagworms are awesome. :D

I love the idea of a construct's heart being some impossible gear. I'm definitely yoinking it.

I love both of these. I have also thought of making dragons as larvae. At that stage they have the natural ability to absorb things from their environment. So young dragons become dragons of the same type as their parents because they are raised around them, but if you stole a baby dragon you could raise it in any environment of your choosing and cultivate it into whatever dragon you like. This isn't just for breath weapon elements either, they can absorb weird things like emotions, dreams, and political intrigue.